Field of the Invention
The present application generally relates to systems and methods for generating molecular formula distributions and models of composition to accommodate limitations of current measurement methods. For example, the systems and methods disclosed herein can be used to extrapolate a molecular formula distribution beyond a boiling point threshold or similar limitation.
Description of Related Art
Petroleum streams are complex mixtures of hydrocarbons containing enormous numbers of distinct molecular species. These streams include a variety of hydrocarbon streams from processes directed to the petroleum molecular composition. For example, virgin petroleum crude oils can contain molecules of a wide boiling point range from highly volatile C4 hydrocarbons to nonvolatile asphaltenes. The streams are extremely complex, and have numerous distinct molecular species. As such, any molecular approximation of the composition is essentially a model, that is, a model of composition (MoC). Analysis of petroleum composition of various boiling points is necessary for inputs to many subsequent processes.
Fourier Transform Ion Cyclotron Resonance (FTICR) mass spectrometry, together with a suitable ionization method, can be used in constructing an initial estimate of the composition of a petroleum stream. Ionization methods used in conjunction with FTICR include Atmospheric Pressure Photoionization (APPI) and negative and positive ion electrospray (N-, PESI).
Despite FTICR's ultra-high mass resolution, this technique alone cannot provide sufficient information to construct an accurate model of composition beyond certain thresholds. For example, none of the identified ionization methods can efficiently ionize molecules in complex hydrocarbon mixtures that boil above 1250° F. Thus, known techniques cannot provide sufficient information to construct a Heavy Hydrocarbon Model of Composition (HHMoC) that is consistent with all features of the petroleum stream. HHMoC, as used herein, refers to a model of composition for a vacuum residuum (also known as resid) stream, i.e., petroleum streams that boil above 1000° F. In at least some resid streams, at least 50 weight percent of the molecules are known to boil above 1250° F. Thus, current ultrahigh resolution APPI-FTICR-MS (or N—, PESI-FTICR-MS) data does not lead to accurate estimates of molecular property distributions on the entire resid, or the entire resid fraction. Examples of FTICR-MS data based on the current technique are disclosed in available literature. See, e.g., McKenna, A. M., et al., “Heavy Petroleum Composition. 1. Exhaustive Compositional Analysis of Athabasca Bitumen HVGO Distillates by Fourier Transform Ion Cyclotron Mass Spectrometry: A Definitive Test of the Doduszynski Model,” Energy & Fuels, v. 24, pp. 2429-2938, 2010.
Furthermore, APPI-FTICR-MS has poor ionization efficiency for molecules that boil above 1250° F. Relative to high-temperature Simdis measurements, FTICR severely under-predicts the amount of material boiling above 1250 F. Hence, it is not uncommon for FTICR to be unable to detect approximately 40 weight percent of the highest boiling material of a resid.
Therefore, there is a need for a system and method to extrapolate a significant portion of the FTICR mass spectrum to higher boiling points such that it is suitable for HHMoC applications.